Heat diffusing device and method of producing the same

ABSTRACT

A heat diffusing device includes first and second metallic thin plates that are alternately laminated to each other, and that are joined along with an upper sealing metallic thin plate and a lower sealing metallic thin plate by diffusion joining so as to form a sealed space in an interior defined by the first and second thin plates and the upper and lower sealing metallic thin plates. A C-shaped groove defined by a steep wall face is formed at a wall face defining the sealed space due to a difference (Δw) between the dimensions of the first metallic thin plates and the dimensions of the second metallic thin plates.

CROSS REFERENCES TO RELATED APPLICATIONS

The present invention contains subject matter related to Japanese Patent Application JP 2007-188373 filed in the Japanese Patent Office on Jul. 19, 2007, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat diffusing device that restricts the temperature of a heat source to a temperature less than or equal to a predetermined temperature by diffusing heat of the heat source in, for example, an electronic apparatus or other apparatuses.

2. Description of the Related Art

Hitherto, in, for example, an electronic apparatus, such as a personal computer or a projector (display apparatus), a heat diffusing device for dissipating heat of a heat source is required. What is called a heat pipe is known as an example of the heat diffusing device. The heat pipe has, for example, the following structure. That is, for example, as shown in FIG. 23, in a heat pipe 1, a plurality of grooves 3, disposed in parallel along a longitudinal direction, are formed at the inner side of a metallic pipe 2 so that their cross sections in a circumferential direction are uneven. In addition, a wick 4, formed of wires, is disposed at the inner sides of the grooves 3, and water 4 is sealed in the grooves 3. When one end of the heat pipe 1 contacts a heat source, the water in the grooves 3 evaporates at this one end, and the steam instantaneously spreads to the other end side. The other end side is in contact with outside air. Therefore, heat exchange occurs, thereby cooling and condensing the steam back into water. This water flows through the wick 4, and returns to the one end. By repeatedly evaporating, condensing, and returning the water, the temperature rise of the heat source is restricted.

Japanese Unexamined Patent Application No. 2004-198098 discloses an example of a heat pipe.

SUMMARY OF THE INVENTION

In the above-described heat pipe 1, as shown in FIG. 22, if the grooves 3 are defined by steep wall faces, that is, right-angled wall faces, a contact angle θ of water 10, in each grooves 3, with respect to a wall face 3 a becomes small, so that a thin portion 9 of the water 10 tends to evaporate. Therefore, the temperature of the wall face at this portion 9 can be made very low. At the same time, capillary action makes it possible to pass the condensed water 10 through the grooves 3, and to return it to an evaporation portion side. However, actually, since the pipe 2 having the plurality of grooves 3 is formed by a drawing process, the grooves 3 defined by steep wall faces cannot be formed. Therefore, the wick 4, formed of wires, is required.

As shown in FIG. 21A, a planar heat diffusing device 11 may be formed. In the heat diffusing device 11, a plurality of grooves 3 are formed by etching a surface of a first metallic thin plate 12. A second metallic thin plate 14, serving as a cover, is joined to the first metallic thin plate 12, to form sealed spaces defined by the grooves 13. The grooves 13 are filled with water 15 under reduced pressure in an initial state. However, as shown in FIG. 21B, when the grooves 13 are formed by etching, the cross sections of the grooves become curved. As a result, grooves defined by steep wall faces cannot be formed.

In view of the aforementioned points, it is desirable to provide a heat diffusing device which makes it possible to precisely form grooves defined by steep wall faces and to provide good heat diffusion, and a method of producing the same.

According to an embodiment of the present invention, there is provided a heat diffusing device including first metallic thin plates and second metallic thin plates, an upper sealing metallic thin plate, and a lower sealing metallic thin plate. The dimensions of the first metallic thin plates are different from dimensions of the second metallic thin plates. The first and second metallic thin plates are alternately laminated to each other, and are joined along with the upper and lower sealing metallic plates by diffusion joining so that a sealed space is formed in an interior defined by the first and second metallic thin plates and the upper and lower sealing metallic plates. A groove defined by a steep wall face is formed at the wall face defining the sealed space due to the difference between the dimensions of the first and second metallic thin plates. A liquid is sealed in the groove under reduced pressure in an initial state.

In the embodiment of the present invention, since the first and second metallic thin plates whose dimensions differ are alternately laminated, a groove defined by a steep wall face is formed with good precision at the wall face defining the sealed space. Since a contact angle θ of the liquid with respect to the wall face defining the groove can be made small, water is efficiently evaporated.

According to another embodiment of the present invention, there is provided a method of producing a heat diffusing device including the following steps. That is, the method includes alternately laminating first and second metallic thin plates to each other, and disposing sealing metallic thin plates at a top side and a bottom side of the laminated first and second metallic thin plates, dimensions of the first metallic thin plates being different from dimensions of the second metallic thin plates. In addition, the method includes forming an integrated laminated body by subjecting the first and second metallic thin plates and the sealing metallic thin plates to diffusion bonding, forming a sealed space in an interior of the laminated body, and forming a groove at a wall face of the sealed space due to the difference between the dimensions of the first and second metallic thin plates, the groove being defined by the steep wall face. Further, the method includes sealing a liquid in the groove in an initial state in which pressure in the sealed space is reduced.

In the method of producing a heat diffusing device according to another embodiment of the present invention, the first and second metallic thin plates whose dimensions differ are alternately laminated, so that a groove defined by a steep wall face can be formed with good precision at the wall face defining the sealed space. When the groove is filled with the liquid, the groove can be filled with the liquid while a contact angle θ of the liquid with respect to the wall face defining the groove is small.

According to the heat diffusing device according to one embodiment of the present invention, a groove defined by steep wall face is formed, and the liquid in the groove can be evaporated with good efficiency. Therefore, a heat diffusing device providing good heat diffusion can be provided.

According to the method of producing a heat diffusing device according to another embodiment of the present invention, a groove defined by a steep wall face can be formed with good precision. Therefore, a heat diffusing device providing good heat diffusion can be produced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are, respectively, a partly cutaway plan view and side view of a heat diffusing device according to a first embodiment of the present invention;

FIGS. 2A and 2B are, respectively, a plan view of an upper sealing metallic thin plate according to the first embodiment, and a sectional view taken along line IIB-IIB thereof;

FIGS. 3A and 3B are, respectively, a plan view of a first metallic thin plate according to the first embodiment, and a sectional view taken along line IIIB-IIIB thereof;

FIGS. 4A and 4B are, respectively, a plan view of a second metallic thin plate according to the first embodiment, and a sectional view taken along line IVB-IVB thereof;

FIGS. 5A and 5B are, respectively, a plan view of a lower sealing metallic thin plate according to the first embodiment, and a sectional view taken along line VB-VB thereof;

FIG. 6 is an enlarged sectional view of a peripheral portion in the heat diffusing device according to the first embodiment;

FIGS. 7A and 7B are, respectively, an enlarged sectional view and an enlarged plan view of a central portion in the heat diffusing device according to the first embodiment;

FIG. 8 is a perspective view of radiating portions in the heat diffusing device according to the first embodiment;

FIG. 9 is a partly cutaway plan view of a liquid supplying portion and a liquid/gas discharging portion of the heat diffusing device according to the first embodiment;

FIGS. 10A and 10B are, respectively, an exploded perspective view of an exemplary liquid supplying portion and an exemplary liquid/gas discharging portion, and a sectional view taken along line XB-XB thereof;

FIG. 11 is a sectional view of a main portion showing the relationship between a groove defined by a steep wall face and a sealed liquid according to the embodiment of the present invention;

FIG. 12 is a partly cutaway plan view of a heat diffusing device according to a second embodiment of the present invention;

FIGS. 13A and 13B are respectively, a sectional view taken along line XIIIA-XIIIA of FIG. 12, and a sectional view taken along line XIIIB-XIIIB of FIG. 12;

FIGS. 14A, 14B, and 14C are, respectively, a perspective view of a first metallic thin plate according to the second embodiment, a sectional view taken along line XIVB-XIVB thereof, and a sectional view taken along line XIVC-XIVC thereof;

FIGS. 15A, 15B, and 15C are, respectively, a perspective view of a second metallic thin plate according to the second embodiment, a sectional view taken along line XVB-XVB thereof, and a sectional view taken along line XVC-XVC thereof;

FIG. 16 is a perspective view of an upper sealing metallic thin plate according to the second embodiment;

FIGS. 17A and 17B are, respectively, a perspective view of a lower sealing metallic thin plate according to the second embodiment, and a sectional view taken along line XVIIB-XVIIB thereof;

FIG. 18 is an exploded perspective view of a main portion showing an exemplary liquid supplying portion and an exemplary liquid/gas discharging portion in the heat diffusing device according to the second embodiment;

FIG. 19 is a sectional view of the main portion of the liquid supplying portion and the liquid/gas discharging portion in the heat diffusing device according to the second embodiment;

FIG. 20 is a perspective view of the main portion after sealing the liquid supplying portion and the liquid/gas discharging portion in the heat diffusing device according to the second embodiment;

FIGS. 21A and 21B are, respectively, a partly cutaway perspective view of a comparative-example heat diffusing device, and a sectional view taken along line XXIB-XXIB thereof;

FIG. 22 is a sectional view of an ideal groove shape; and

FIG. 23 is a partly sectional perspective view of a related heat pipe.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will hereunder be described with reference to the drawings.

FIGS. 1 to 5 illustrate a heat diffusing device and a method of producing the same according to a first embodiment of the present invention. As shown in FIGS. 1A and 1B, a heat diffusing device 21 according to the embodiment includes a laminated body 24 and sealing metallic plates 25 and 26. The laminated body 24 includes first metallic thin plates 22 and second metallic thin plates 23, which are alternately laminated, and which have rectangular contour shapes, that is, rectangular contour shapes of the same size in the embodiment, as viewed from above. The dimensions of the second metallic thin plates 23 differ from those of the first metallic thin plates 22. The sealing metallic thin plates 25 and 26 seal the top and bottom of the laminated body 24, respectively. The first and second metallic thin plates 22 and 23 have the same film thickness. The upper and lower sealing metallic thin plates 25 and 26 also have the same film thickness.

As shown in FIGS. 3A and 3B, each first metallic thin plate 22 has a pattern including a central portion 31, a rectangular frame peripheral portion 32, and a plurality of radiating portions communicating with the peripheral portion 32 from the central portion 31. In the embodiment, there are four radiating portions 33 (331, 332, 333, and 334) that radiate in the form of a cross so as to divide each of the four sides into two equal parts. The peripheral portion 32 has the same width over the entire periphery, and a predetermined width w1 is selected as its width. The radiating portions 331 to 334 have a same width d1 up to respective certain points from the peripheral portion 32, and taper so that their widths are gradually decreased towards the central portion 31 from their respective certain points. In the embodiment, the radiating portions 33 (331 to 334) are formed linearly symmetrically. Four through holes 35, which receive support columns formed integrally with the lower sealing metallic thin plate 26 (described later), are formed in the four radiating portions 331 to 334, respectively. The first metallic thin plates 22 can be formed by pressing one metallic thin plate.

As shown in FIGS. 4A and 4B, each second metallic thin plate 23 has a pattern including a central portion 36, a rectangular frame peripheral portion 37, and a plurality of radiating portions communicating with the peripheral portion 37 from the central portion 36. In the embodiment, there are four radiating portions 38 (381, 382, 383, and 384) that radiate in the form of a cross in which two diagonals intersect each other. That is, the pattern of each second metallic thin plate 23 differs from the pattern of each first metallic thin plate 22 in its radiating portions. The peripheral portion 37 has the same width over the entire periphery, and a predetermined width w2, which is smaller than the width w1 in each metallic thin plate 22 (w1>w2), is selected as its width. The radiating portions 381 to 384 have a same width d2 up to respective certain points from the peripheral portion 37, and taper so that their widths are gradually decreased towards the central portion 36 from their respective certain points. In the embodiment, the radiating portions 38 (381 to 384) are formed linearly symmetrically. Four through holes 39, which receive support columns formed integrally with the lower sealing metallic thin plate 26 (described later), are formed in the four radiating portions 381 to 384, respectively. The first metallic thin plates 23 can be formed by pressing one metallic thin plate.

The width d1 of each radiating portion 33 of each first metallic thin plate 22 and the width d2 of each radiating portion 38 of each second metallic thin plate 23 may be the same (d1=d2), or may be different from each other (d1≠d2). It is desirable that the diameters of the through holes 35 and 39 of the radiating portions 33 and 38 of the respective first and second metallic thin plates 22 and 23 be the same.

Since the width w1 of the peripheral portion 32 of each first metallic thin plate 22 and the width w2 of the peripheral portion 37 of each second metallic thin plate 23 differ from each other, a dimension difference Δw=w1−w2 occurs at the peripheral portions 32 and 37 at the inner side when they are laminated.

As shown in FIG. 2, the upper sealing metallic thin plate 25 has a rectangular shape, and has through holes 41, which receive ends of the support columns, at locations corresponding to the radiating portions 33 and 38 of the respective first and second metallic thin plates 22 and 23, that is, at locations corresponding to the support columns formed integrally with the lower sealing metallic thin plate 26. In the embodiment, eight through holes 41 are formed.

As shown in FIG. 5, the lower sealing metallic thin plate 26 has a rectangular shape, and has support columns 42 integrally provided upright at locations corresponding to the through holes 41 of the upper sealing metallic thin plate 25 and the through holes 35 and 39 of the radiating portions 33 and 38 of the respective first and second metallic thin plates 22 and 23. In the embodiment, eight support columns 42 are formed. The support columns 42 have large-diameter portions 42 a, which are inserted into the through holes 35 and 39 of the radiating portions 33 and 38 of the respective first and second metallic thin plates 22 and 23, and small-diameter portions 42 b, which are inserted into the through holes 41 of the upper sealing metallic thin plate 25, at ends of the large-diameter portions 42 a. The support columns 42 withstand internal pressure to maintain the interval between the lower sealing metallic thin plate 26 and the upper sealing metallic thin plate 25. The support columns 42 may not be joined to the radiating portions 33 and 38. Instead, they may pass through the radiating portions 33 and 38. The support columns 42 may be omitted. The eight support columns are subjected to diffusion bonding simultaneously with the laminated structure, thereby connecting the upper and lower planar surfaces. FIG. 5 shows that, for ensuring strength, a caulking mechanism may also be used.

The first and second metallic thin plates 22 and 23, the upper sealing metallic thin plate 25, and the lower sealing metallic thin plate 26 are formed of a metal allowing diffusion bonding, such as copper or beryllium copper. In the embodiment, they are formed of copper.

In the embodiment, the laminated body 24 is formed by alternately laminating a plurality of the first and second metallic thin plates 22 and 23 (for example, 21 thin plates) so that the first metallic thin plates 22 are disposed at the uppermost layer and the lowermost layer. The laminated body 24 is disposed on the lower sealing metallic thin plate 26. That is, the laminated body 24 is disposed on the lower sealing metallic thin plate 26 so that the large-diameter portions 42 a of the support columns 42 of the lower sealing metallic thin plate 26 are inserted into the through holes 35 and 39 of the respective radiating portions 33 and 38 of the laminated body 24. The upper sealing metallic thin plate 25 is disposed on the laminated body 24. The upper sealing metallic thin plate 25 is disposed on the laminated body 24 so that the small-diameter portions 42 b at the ends of the support columns 42, integrally formed with the lower sealing metallic thin plate 26, are inserted into the through holes 41.

In addition, in the embodiment, the laminated body 24, having the sealing metallic thin plates 25 and 26 disposed at the top and bottom sides thereof, is, in this state, pressed and heated in a vacuum. This causes the laminated body 24 to be formed into an integrated structure by diffusion bonding, so that the laminated structure 24 is air-tightly and liquid-tightly sealed. The support columns 42 are bonded to the upper sealing metallic thin plate 25 by diffusion bonding while stepped surfaces at the ends of the support columns 42 are in contact with the back surface of the upper sealing metallic thin plate 25. At the same time, grooves (described later), which are formed at side wall faces at sealed spaces in the laminated body 24, are filled with a liquid, which becomes a refrigerant under reduced pressure in an initial state. Accordingly, the heat diffusing device 21 is formed.

In the heat diffusing device 21 according to the first embodiment, as shown in FIG. 6, grooves 44 defined by steep wall faces are formed at side walls of peripheral portions 28 in sealed spaces 45 in FIG. 1 due to the difference Δw between the dimensions of the first and second metallic thin plates 22 and 23. That is, the C-shaped grooves 44 defined by upper and lower wall faces that are at right angles with respect to respective back wall faces as viewed in cross section of the grooves are formed. In addition, as shown in FIGS. 7A and 7B, grooves 44 defined by steep wall faces are formed at side wall faces of respective central portions 27 in the sealed spaces 45 due to the difference Δw between the dimensions of the first and second metallic thin plates 22 and 23. That is, the C-shaped grooves 44 defined by upper and lower wall faces that are at right angles with respect to respective back wall faces as viewed in cross section of the grooves are formed. The grooves 44 are formed at the central portions 27 in accordance with the star-shapes of the central portions 27 as indicated by an alternate long and short dash line 29 as viewed from the top.

In the first metallic thin plates 22 disposed at the upper and lower sides of their corresponding second metallic thin plates 23, flow paths 51 are formed between the upper and lower radiating portions 33 (331 to 334). The flow paths 51 are provided for a return liquid (described later), and have small intervals providing capillary action. Similarly, in the second metallic thin plates 23 disposed at the upper and lower sides of their corresponding first metallic thin plates 22, flow paths 52 are similarly formed between the upper and lower radiating portions 38 (381 to 384). The flow paths 52 are provided for a return liquid, and have small intervals providing capillary action. (Refer to FIG. 8.)

It is desirable that the liquid, which becomes a refrigerant, be, for example, water (pure water). As shown in FIG. 11, a width t1 (corresponding to the thickness of each second metallic thin plate 23) of each groove 44, and a depth Δw thereof can be freely set in accordance with the refrigerant. For example, when water is used as the refrigerant, the groove width t1 is optimally from 20 μm to 100 μm. However, depending upon the surface tension of the refrigerant, the groove width t1 is not limited to this value.

Next, the operation of filling the interior of the heat diffusing device 21 with the liquid will be described in detail with reference to FIGS. 9 and 10. As shown in FIG. 9, a liquid supplying portion 54 and a liquid/gas discharging portion 55 are previously provided at, for example, respective corners that oppose each other on a diagonal of the heat diffusing device that is integrally formed by diffusion bonding. As shown in FIGS. 10A and 10B, the liquid supplying portion 54 and the liquid/gas discharging portion 55 have the same grooved structure. Each of the liquid supplying portion 54 and the liquid/gas discharging portion 55 is formed as follows. For example, two notches 56 a and 56 b communicating with the sealed space 45 are formed at respective locations of the uppermost first metallic thin plate 22, and a groove 57 whose ends communicate with the notches 56 a and 56 b at the lower side of the upper sealing metallic thin plate 25 are formed in the upper sealing metallic thin plate 25. In addition, a through hole 58 communicating with the outside from the groove 57 is formed in the upper sealing metallic thin plate 25.

The upper sealing metallic thin plate 25, the laminated body 24, and the lower sealing metallic thin plate 26 are disposed in layers and subjected to diffusion bonding, and formed in a sealed state as mentioned above. Then, liquid, such as water, is supplied from the through hole 58 of the liquid supplying portion 54 to the interior of the sealed space 45 through the groove 57 and the notches 56 a and 56 b. The liquid can be supplied so as to fill up the interior of the sealed space 45. In this state, both sides of the groove 57 on respective sides of the through hole 58 in the liquid supplying portion 54 are temporarily pressed inwards by, for example, stupid caulking, to seal the liquid supplying portion 54. Then, the liquid in the sealed space 45 is sucked out and discharged from the through hole 58 of the liquid/gas discharging portion 55, and is exhausted. This causes a portion of the liquid to remain in the groove 44 at the wall face defining the sealed space while the pressure in the interior of the sealed space 45 is in a reduced state. In this state, both sides of the groove 57 on the respective sides of the through hole 58 in the liquid/gas discharging portion 55 are pressed inwards by, for example, stupid caulking, to seal the liquid/gas discharging portion 55. Reference numerals 59 in FIG. 10A denote caulking positions. At the end of this process, the heat diffusing device 21 according to the first embodiment is completed.

Next, the operation of the heat diffusing device 21 according to the first embodiment will be described. First, as shown in FIG. 11, in the heat diffusing device 21, the groove 44, formed at the wall face defining the sealed space, has a cross-section rectangular shape defined by a vertical wall face, which is an ideal groove shape. When this groove 44 is filled with water 100 (which is a refrigerant), a contact angle θ of the water 100 with respect to a wall face 44 a is less than 40° (θ<40°). Since the contact angle θ of the water 100 is reduced, the water 100 is in a state in which a thin portion 101 adhered to an open side tends to evaporate.

In the heat diffusing device 21, a heat source is disposed at the central portions 27. What is called a point heat source is disposed. The peripheral portions 28 of the heat diffusing device 21 operate as heat-exhausting portions, that is, cooling portions. When the central portions 27 of the heat diffusing device 21 generate heat using the heat source, the water 100 in the grooves 44 at portions corresponding to the central portions 27 evaporates, and is turned into steam. Steam radiation is performed with respect to the wide sealed spaces 45 (see FIG. 1), so that the steam instantaneously flies towards the peripheral portions 28. The steam is cooled by the peripheral portions 28 (that is, the steam heat is exhausted at the heat-exhausting portions at the other end), and is condensed back to water. The resulting water enters the grooves 44 at the peripheral portions 28. When the width t1 of the cross-section rectangular groove 44 shown in FIG. 11 is on the order of from 20 μm to 100 μm, the water that has entered the linear groove 44 spreads in the groove 44 due to capillary action. Therefore, the water that has entered the grooves 44 at the peripheral portions 28 and become a return liquid flows through the grooves 44. Then, it flows between the radiating portions 33 and 33 and between the radiating portions 38 and 38 by capillary action, and returns to the grooves 44 at the central portions 27. The spaces between the radiating portions 33 and 33 and between the radiating portions 38 and 38 are formed as return flow paths. The narrow spaces between the radiating portions 33 and 33 and between the radiating portions 38 and 38 operate as wicks that widely diffuse the water.

According to the heat diffusing device 21, repeatedly evaporating, condensing, and returning the water diffuses the heat, generated at the point of the central portions, to an entire area extending to the peripheries, so that the heat diffusing device 21 is not heated to a temperature greater than or equal to a predetermined temperature. Therefore, it is possible to restrict a temperature rise at the heat source.

FIGS. 12 to 17 show a heat diffusing device and a method of producing the same according to a second embodiment of the present invention. As shown in FIGS. 12 and 13, a heat diffusing device 61 according to the embodiment includes a laminated body 64 and sealing metallic thin plates 65 and 66 that seal the upper and lower sides of the laminated body 64. In the laminated body 64, first metallic thin plates 62 and second metallic thin plates 63 are alternately laminated, and have rectangular shapes in which a long side of a contour shape is sufficiently longer than a short side of the contour shape as viewed from above. The dimensions of each second metallic thin plate 63 differ from those of each first metallic thin plate 62. The first and second metallic thin plates 62 and 63 have the same thickness. The upper sealing metallic thin plate 65 and the lower sealing metallic thin plate 66 also have the same thickness.

As shown in FIGS. 14A to 14C, each first metallic thin plate 62 is formed into a pattern in which a plurality of elongated openings 68, extending in a long-side direction, are formed in parallel in a short-side direction. A long-side width of a peripheral portion 67 is selected so that it is a predetermined width w3, and a short-side width of the peripheral portion 67 is selected so that it is a predetermined width w4. In this case, when the entire periphery of the peripheral portion 67 has the same width, the width w3=the width w4. The width of partitions 69 partitioning the respective openings 68 are selected so that it is a predetermined width w5. The widths of the two short sides of the peripheral portion 67 and the widths of the two long sides of the peripheral portion 67 can be selected so that they are suitable widths as required. Each first metallic thin plate 62 can be formed by pressing one metallic thin plate.

As shown in FIGS. 15A to 15C, each second metallic thin plate 63 is similarly formed into a pattern in which a plurality of elongated openings 71, extending in a long-side direction, are formed in parallel in a short-side direction so as to be positioned in correspondence with the elongated openings 68 of each first metallic thin plate 62. The overall pattern of each second metallic thin plate 63 is similar to that of each first metallic thin plate 62. However, since the overall dimensions of its pattern differs from those of the pattern of each first metallic thin plate 62, its pattern is, properly speaking, different from that of each first metallic thin plate 62.

That is, in each second metallic thin plate 63, the width of a peripheral portion 72 and the width of partitions 73 are smaller than the width of the peripheral portion 67 and the width of the partitions 69 of each first metallic thin plate 62, so that the dimensions of each second metallic thin plate 63 differs from those of each first metallic thin plate 62.

As shown in FIGS. 15A to 15C, in each second metallic thin plate 63, the long-side width of the peripheral portion 72 is selected so that it is a predetermined width w6 that is smaller than the width w3 in each first metallic thin plate 62 (w3>w6). In addition, the short-side width of the peripheral portion 72 is selected so that it is a predetermined width w7 that is smaller than the width w4 in each first metallic thin plate 62 (w4>w7). In this case, when the entire periphery of the peripheral portion 72 has the same width, the width w6=the width w7. The width of partitions 73 partitioning the respective openings 71 are selected so that it is a predetermined width w8 that is smaller than the width w5 in each first thin metallic plate 62. The widths of the two short sides of the peripheral portion 72 and the widths of the two long sides of the peripheral portion 72 can be selected so that they are suitable widths as required. Each second metallic thin plate 63 can be formed by pressing one metallic thin plate.

The long-side width w3 of the peripheral portion 67 of each first metallic thin plate 62 and the long-side width w6 of the peripheral portion 72 of each second metallic thin plate 63 differ from each other. In addition, the short-side width w4 of the peripheral portion of each first metallic thin plate 62 and the short-side width w7 of the peripheral portion 72 of each second metallic thin plate 63 differ from each other. Further, the width w5 of the partitions 69 and the width w8 of the partitions 73 differ from each other. Therefore, at the inner side when they are laminated, dimensional differences Δw=w3−w6, Δw=w4−w7, and Δw=w5−w8 occur in the side wall faces at the elongated openings 68 and 71. That is, the same dimension differences Δw occur over the entire periphery of the wall faces at the elongated openings.

As shown in FIG. 16, the upper sealing metallic thin plate 65 is formed using a rectangular thin plate having a contour shape of a size that is the same as that of the first and second metallic thin plates 62 and 63. The upper sealing metallic thin plate 65 can be formed by pressing one metallic thin plate.

As shown in FIGS. 17A and 17B, the lower sealing metallic thin plate 66 is formed using a rectangular thin plate having a contour shape of a size that is the same as that of the first and second metallic thin plates 62 and 63. The lower sealing metallic thin plate 66 is formed so as to have a plurality of horizontal grooves 75 on both ends of the rectangular shape at the top surface of the lower sealing metallic thin plate 66. The horizontal grooves 75 communicate with the openings 68 of the first metallic thin plate 62 and the openings 71 of the second metallic thin plate 63. The lower sealing metallic thin plate 66 can be formed by pressing one metallic thin plate.

The first and second metallic thin plates 62 and 63, the upper sealing metallic thin plate 65, and the lower sealing metallic thin plate 66 are formed of a metal allowing diffusion bonding, such as copper or beryllium copper. In the embodiment, they are formed of copper.

In the embodiment, the laminated body 64 is formed by alternately laminating a plurality of the first and second metallic thin plates 62 and 63 (for example, 21 thin plates) so that the first metallic thin plates 62 are disposed at the uppermost layer and the lowermost layer. The upper sealing metallic thin plate 65 and the lower sealing metallic thin plate 66 are disposed at the top and the bottom of the laminated body 64. The upper sealing metallic thin plate 65, the laminated body 24, and the lower sealing metallic thin plate 66 are integrated to each other by diffusion bonding as a result of being pressed and heated in a vacuum. Therefore, they are air-tightly and liquid-tightly sealed. At the same time, grooves (described later), which are formed at side wall faces, defining sealed spaces 77 formed by the openings 68 and 71 in the laminated body 64, are filled with a liquid (which becomes a refrigerant under reduced pressure in an initial state). Accordingly, the heat diffusing device 61 is formed.

In the heat diffusing device 61 according to the second embodiment, grooves 78 (see FIGS. 13A and 13B), defined by steep wall faces, are formed over the side wall faces, defining the respective sealed spaces 77 formed by the elongated openings in FIG. 12, due to the dimension difference Δw between the dimensions of the first and second metallic thin plates 62 and 63. The grooves 78 are formed into annular shapes continuously formed with the entire peripheries of the respective sealed spaces 77. Similarly to the first embodiment, as viewed from the cross section of the grooves, the grooves 78 have C shapes having upper and lower wall faces that are at right angles to respective back wall faces.

As mentioned above, it is desirable to use, for example, water (pure water) as the liquid that becomes a refrigerant.

Next, the operation of filling the interior of the heat diffusing device 61 with the liquid will be described in detail with reference to FIGS. 18 to 20. In the embodiment, a liquid supplying portion 81 is previously provided at one end portion side in a longitudinal direction and a liquid/gas discharging portion 82 is previously provided at the other end portion side in the longitudinal direction with respect to the heat diffusing device 61 that is integrally formed by the diffusion bonding. The liquid supplying portion 81 and the liquid/gas discharging portion 82 have the same structure. As shown in FIG. 18, each of the liquid supplying portion 81 and the liquid/gas discharging portion 82 is formed as follows. For example, two notches 83 a and 83 b communicating with the sealed space 77 are formed at, for example, respective locations of the uppermost first metallic thin plate 62 of the laminated body 64. A groove 84 whose ends communicate with the notches 83 a and 83 b at the lower side of the upper sealing metallic thin plate 65 is formed in the upper sealing metallic thin plate 65. In addition, a through hole 85 communicating with the outside from the groove 84 is formed in the upper sealing metallic thin plate 65.

The upper sealing metallic thin plate 65, the laminated body 64, and the lower sealing metallic thin plate 66 are disposed in layers and subjected to diffusion bonding, and formed in a sealed state as mentioned above. Then, liquid, such as water, is supplied from the through hole 85 of the liquid supplying portion 81 to the interior of the sealed space 77 through the groove 84 and the notches 83 a and 83 b. The water is supplied to all of the interiors of the sealed spaces 77 (see FIG. 12) partitioned by the partitions 68 and 73 through the horizontal grooves 75, formed in the inside surface of the lower sealing metallic thin plate. The water can be supplied so that it fills completely the interiors of all of the sealed spaces 77. In this state, both sides of the groove 84 on respective sides of the through hole 85 in the liquid supplying portion 81 are temporarily pressed inwards by, for example, stupid caulking, to seal the liquid supplying portion 81. Then, the liquid in the sealed space 77 is sucked out and discharged from the through hole 85 of the liquid/gas discharging portion 82, and is exhausted. This causes a portion of the liquid to remain in the groove 78 at the wall face defining the sealed space 77 while the pressure in the interior of the sealed space 77 is in a reduced state. In this state, both sides of the groove 84 on the respective sides of the through hole 85 in the liquid/gas discharging portion 82 are pressed inwards by, for example, stupid caulking, to seal the liquid/gas discharging portion 82. Reference numerals 89 in FIG. 10A denote caulking positions. At the end of this process, the heat diffusing device 61 according to the second embodiment is completed.

Next, the operation of the heat diffusing device 61 according to the second embodiment will be described. As discussed with reference to FIG. 11, in the heat diffusing device 61, the grooves 78, formed along the entire peripheries of the side wall faces defining the sealed spaces 77 formed in parallel, have a cross-section rectangular shape having vertical wall faces, which is an ideal groove shape. When the grooves 78 are filled with, for example, water 100 (which is a refrigerant), a contact angle θ of the water 100 with respect to a groove wall face is less than 40° (θ<40°) (see FIG. 11). Since the contact angle θ of the water 100 is reduced as mentioned above, the water 100 is in a state in which a thin portion adhered to an open side tends to evaporate.

In the heat diffusing device 61 according to the second embodiment, a heat source is disposed at one end side thereof. The other end side of the heat diffusing device 61 operates as a heat-exhausting portion, that is, a cooling portion. The linear sealed spaces 77 become gas flow paths, and the grooves 78 at the side wall faces become liquid return flow paths. When the one end portion of the heat diffusing device 61 generates heat using the heat source, the water in the grooves 78 at the one end portion side evaporates, and is turned into steam. Steam radiation is performed with respect to the wide sealed spaces 77, so that the steam instantaneously flies to the other end side. The steam is cooled by the cooling portion at the other end (that is, the steam heat is exhausted at the heat-exhausting portion at the other end), and is condensed back to water. The returned water enters the grooves 78 at the other end portion. When the width of each cross-section rectangular groove 78 is on the order of from 20 μm to 100 μm, the water that has entered the grooves 78 spreads into the long-side grooves 78 from the short side due to capillary action. Therefore, the water returns to the grooves 78 at the one end portion through return flow paths formed by the long-side grooves 78.

According to the heat diffusing device 61, repeatedly evaporating, condensing, and returning the water diffuses the heat, generated at the one end portion, to an entire area extending to the other end portion, so that the heat diffusing device 61 is not heated to a temperature greater than or equal to a predetermined temperature. Therefore, it is possible to restrict a temperature rise at the heat source.

According to the diffusing device 61, the laminated structure, in which the first and second metallic thin plates are alternately laminated to each other, makes it possible to form the grooves 78 defined by steep wall faces. The grooves 78 operate as wicks that widely diffuse water. In the wick structure formed by the grooves 78, the wall faces rise steeply compared to those formed by etching or mechanical processing. Therefore, a heat transport capacity is large as a result of making the contact angle θ of the liquid small.

The heat diffusing device according to the above-described embodiments of the present invention is applicable to, for example, restricting heat generation in an electronic apparatus. For example, the heat diffusing device according to the embodiments is suitable for use in restricting heat generation of a light-emitting diode of a projector or heat generation in a central processing unit (CPU) in a personal computer.

It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof. 

1. A heat diffusing device comprising: first metallic thin plates and second metallic thin plates, dimensions of the first metallic thin plates being different from dimensions of the second metallic thin plates; an upper sealing metallic thin plate; and a lower sealing metallic thin plate, wherein the first and second metallic thin plates are alternately laminated to each other, and are joined along with the upper and lower sealing metallic plates by diffusion joining so that a sealed space is formed in an interior defined by the first and second metallic thin plates and the upper and lower sealing metallic plates, wherein a groove defined by a steep wall face is formed at a wall face defining the sealed space due to the difference between the dimensions of the first and second metallic thin plates, and wherein a liquid is sealed in the groove under reduced pressure in an initial state.
 2. The heat diffusing device according to claim 1, wherein the sealed space is rectangular, wherein the groove communicates with an entire periphery of the sealed space, and wherein one end portion side of the sealed space in a longitudinal direction is an evaporation portion, and the other end portion side of the sealed space in the longitudinal direction is a heat-exhausting portion.
 3. The heat diffusing device according to claim 2, wherein a plurality of the rectangular sealed spaces are disposed in parallel.
 4. The heat diffusing device according to claim 1, wherein the first and second metallic thin plates each have a plurality of radiating portions communicating with respective peripheral portions from respective central portions of the first and second metallic thin plates, wherein a radiating-portion pattern of each first metallic thin plate differs from a radiating-portion pattern of each second metallic thin plate, wherein a flow path for a return liquid is disposed between the radiating portions of the metallic thin plates of one type that are laminated to each other so that the metallic thin plates of the one type are disposed on both sides of the metallic thin plates of the other type, and wherein each central portion is the evaporation portion, and each peripheral portion is the heat-exhausting portion.
 5. The heat diffusing device according to claim 1, wherein the first and second metallic thin plates and the sealing metallic thin plates are formed of a same material.
 6. A method of producing a heat diffusing device comprising the steps of: alternately laminating first and second metallic thin plates to each other, and disposing sealing metallic thin plates at a top side and a bottom side of the laminated first and second metallic thin plates, dimensions of the first metallic thin plates being different from dimensions of the second metallic thin plates; forming an integrated laminated body by subjecting the first and second metallic thin plates and the sealing metallic thin plates to diffusion bonding, forming a sealed space in an interior of the laminated body, and forming a groove at a wall face of the sealed space due to the difference between the dimensions of the first and second metallic thin plates, the groove being defined by a steep wall face; and sealing a liquid in the groove in an initial state in which pressure in the sealed space is reduced.
 7. The method of producing the heat diffusing device according to claim 6, wherein thin plates each having a rectangular opening and a peripheral portion at the opening are used as the first and second metallic thin plates, the peripheral portions having different widths, wherein thin plates having areas allowing the openings to be closed are used as the upper and lower sealing metallic thin plates, and wherein the groove communicating with an entire periphery of the sealed space, formed by the openings, is formed.
 8. The method of producing the heat diffusing device according to claim 7, wherein thin plates each having a plurality rectangular openings disposed in parallel are used as the first and second metallic thin plates.
 9. The method of producing the heat diffusing device according to claim 6, wherein thin plates each having a plurality of radiating portions communicating with a peripheral portion from a central portion, and each having an opening between the radiating portions, are used as the first and second metallic thin plates, patterns of the radiating portions of the thin plates differing from each other, wherein the sealed space is formed by the openings, and wherein the groove is formed at the central portion and the peripheral portion of each thin plate.
 10. The heat diffusing device according to claim 6, wherein the first and second metallic thin plates and the sealing metallic thin plates are formed of thin plates of a same material. 